Rubber waste, and particularly tire rubber waste, is an area of increasing concern for a number of reasons. Accordingly, substantial efforts are made to develop and implement methods of recycling waste rubber as a way to reduce the environmental impact and the amount of virgin rubber used. Various uses for ground rubber have been developed, such as, for example, as fuel and use in running tracks and other high impact and high traffic surfaces.
In other instances waste rubber may be mixed with virgin rubber to form new rubber products. The waste rubber may be mixed with the virgin rubber in particle form, or may be reclaimed, also sometimes referred to as devulcanized, to allow the recycled rubber to bond with the virgin rubber during vulcanization. Prior art rubber products and methods of making rubber products including recycled rubber have focused on providing a reclaimed rubber with a lower Mooney viscosity in order to provide better processability. A significant expense in producing reclaimed rubber can be grinding the rubber particles prior to the reclamation process. In addition, the levels of low Mooney viscosity reclaimed rubber that can be used in a new rubber product is limited due to a reduction in performance characteristics of the product if too much reclaimed rubber having a low Mooney viscosity is introduced.
It is known in the tire art to use reclaimed rubber in new products, including tire treads and tire tread compounds. Generally, reclaimed rubber refers to rubber that has been crosslinked and subsequently treated to break down the crosslinked network and thereby make the rubber processable. The treatment may break or sever the sulfur crosslinks and/or sever the polymer chains.
As known in the art, reclaimed rubber has been used in the manufacture of retreads, which are tire treads applied over a used tire carcass that has been prepped by removing any of the original tread. The cost of reclaimed rubber can, however, deter its use. One factor driving the cost of reclaimed rubber is the degree to which the rubber is treated. Conventional wisdom suggests treating the cured rubber to an extent that the reclaimed rubber has properties, such as the ability to be mixed, that are similar to virgin rubber.
Other challenges in using reclaimed rubber include the relative amount of reclaimed rubber that may be used in the tire tread compound. Currently, the amount employed is a relatively small percentage of the total rubber included because greater amounts of reclaimed rubber have resulted in unacceptable characteristics and performance of the tire tread.
The ability to use reclaimed rubber nonetheless remains desirable and therefore there is a need to address the problems that currently exist in the art . . .